When ozone pollution skyrocketed in the tiny town of Boulder, Wyo., in 2008, it was relatively easy to identify the culprit as oil and gas drilling, the only major industry in the rural area.
Today, a similar situation in San Antonio, Texas, will be more difficult to resolve. The city has violated federal ozone standards dozens of times since 2008, but with so much industrial activity in and around the city—including the Eagle Ford shale drilling boom south of San Antonio—local officials are waiting for the results of a state-funded study to pinpoint the source of the pollution.
San Antonio's ozone problem is so serious that the U.S. Environmental Protection Agency could designate the city a nonattainment area for ozone, a hazardous air pollutant that can cause serious respiratory problems. If that happens, the growing city would likely be saddled with additional air quality regulations, including stricter pollution controls on vehicles and industrial plants.
The EPA's ambient air quality standard for ozone is 75 parts per billion (ppb). Since 2012, San Antonio's ozone monitors have detected concentrations as high as 87 ppb.
The ozone study will include an emission inventory of all pollution sources in the region. The final report, due in December, is expected to determine how much of the problem is caused by drilling in the Eagle Ford, arguably the nation's largest oil and gas development.
Peter Bella, natural resources director of the Alamo Area Council of Governments, the group behind the study, said it's premature to blame shale drilling for the city's ozone problems. AACOG serves 12 counties, including five in the Eagle Ford shale.
"It's a long process to try and figure out what the heck's going on," Bella said. "I think what we have to do, out of a sense of fairness and accuracy, is to complete our emissions inventory [of the Eagle Ford] and place it into the context of the rest of our inventory."
Elena Craft, a health scientist at the nonprofit Environmental Defense Fund, said San Antonio has a tough road ahead even if it brings itself back into compliance. The EPA is expected to tighten the ozone standard in the next few years, making it that much harder to keep San Antonio out of nonattainment.
"When you go into nonattainment, it is something of an admission that state and local folks weren't able to make the requirements and reductions to maintain compliance," Bella said "In a certain sense, it's saying the federal government is taking the reins."
Ozone levels in San Antonio began rising in 2007, with the steepest increase seen around 2011, just as the Eagle Ford boom exploded. The heaviest drilling in the 400-by-50 mile shale play lies 50 miles southeast of the city, and the wind often blows from the southeast.
But of the three ozone monitors San Antonio uses to collect data on ozone compliance, the monitor closest to the shale play also records the lowest ozone concentrations. And the culprit could even be farther away, because studies have shown that emissions from power plants can travel hundreds of miles.
Still, drilling in the Eagle Ford is an important factor.
Previous studies show that emissions of ozone-forming chemicals from sources other than drilling have dropped significantly since 2007 despite the city's population growth, said Steven Smeltzer, AACOG's environmental manager. Smeltzer attributes the improvement to new vehicle standards and voluntary reductions by local industries.
Preliminary numbers from the AACOG study also indicate that much of the problem lies in the Eagle Ford. InsideClimate News obtained a copy of the data, which have not been made public. The data show that during the months when San Antonio experiences the highest ozone levels—April through October—oil and gas development produced about half the amount of ozone-forming emissions per day as all other industrial sources combined.
Bella said the data came from an early version of the study that wasn't as thorough as later drafts. "My sense is they're really not worth using...They're not solid numbers."
He declined to comment on whether the numbers are close to the latest estimates. What matters isn't the number, he said, but the process behind the study. If the science isn't right, then it's "garbage in, garbage out."
Pinpointing Ozone Sources Is Difficult
The San Antonio study poses many technical challenges for the scientists involved.
Ground-level ozone is formed when nitrous oxides (NOx) react with volatile organic compounds (VOCs) in the presence of heat and sunlight. Instead of looking directly for ozone, scientists must track emissions of NOx and VOCs and analyze how they react and move in the atmosphere. Both types of chemicals are released by the burning of fossil fuels. VOCs are also emitted from other sources, including oil and gas wells.
Some sources are easier to trace than others. Power plants, for instance, regularly collect data on what's emitted from smokestacks. And vehicle registration data can be used to calculate emissions from cars and trucks. But it's much harder to track sources like VOC-emitting house paints and the collective contributions of drilling equipment used in the Eagle Ford.
"What we would love to do is go out to the site, write down the description of every engine, generator, pump, everything that burns fossil fuels, get a description of the horsepower, load factor, the whole nine yards...[and] do a complete inventory on a site by site basis," Bella said. But because his team has limited time and resources, "clearly that's impossible."